1. Field of the Invention
The present invention relates to slidable homokinetic joints which may be used in particular in lateral transmissions of motor vehicles which have a front-wheel drive or a drive through independent wheels.
2. Description of the Prior Art
It is known that internal combustion engines are the center of vibrations of amplitudes which vary within a wide frequency band, on the order of 30 to 300 hertz. A slidable homokinetic joint should not only transmit the torque at an operating angle and with variable elongations, but also be axially infinitely permeable, both for a zero operating angle and at a maximum operating angle, so as to prevent the axial components of the vibrations of the engine to travel toward the driving wheel and the structure of the vehicle. Lastly, it should not, when it operates at an operating angle, itself introduce a periodic axial excitation capable of initiating vibrations in the structure of the vehicle.
Now, due to operating frictions whose amplitude varies cyclically, known slidable homokinetic joints have the following drawbacks:
The moments perpendicular to the axis of rotation produced by the frictions vary periodically and create corresponding excitations which may cause resonances in the structure of the vehicle or in the transmission shaft itself.
These periodic variations of friction result from the manner in which the rolling members move which, depending on the considered phase angle, roll or slide under a high load and thus bring about very high fluctuations in the resulting moment. Such an operation, in which is given rolling body (such as a ball) passes from a practically pure rolling motion to a total sliding motion is completely different from that of a ball bearing in which the sliding rate is low and practically constant.
There is known from French patent application No. FR-A-81 10 796 (French Patent No. 2,506,872), a slidable homokinetic joint which has for its purpose to overcome the drawbacks mentioned hereinbefore and which proposes various modifications, all of which have the feature of comprising three pairs of rolling planes evenly angularly spaced about a first axis, the planes of each pair being parallel to each other and to this fixed axis, these rolling planes cooperating with needles interposed between the pairs of planes and intermediate elements, moreover in contact by sperhical bearing surfaces which are complementary with journals evenly anglarly spaced apart and extending radially relative to the axis of a second element.
Such a joint constitutes a notable progress but it has been found that, when operating at an angle, the needles are made to slide in their plane so that it is necessary to provide means for retaining them laterally, which rather complicates the manufacture. Further, frictions occur between the ends of the needles and the retaining means, which is of course disadvantageous.
As in the joint briefly described hereinbefore, the invention proposes to provide a telescopically slidable homokinetic joint in which the vibrations coming from the driving element are filtered absorbed and which is moreover devoid or substantially devoid of periodic internal frictions. On the contrary, the object is to obtain a moment of friction which is constant in magnitude and direction, and a sliding with a very high degree of freedom irrespective of the angle at which the joint operates, it being moreover ensured that the latter does not produce periodic axial stresses. Further, the specific drawbacks due to the presence of needles must also be eliminated.
The invention therefore provides a homokinetic joint comprising a first element arranged along a first axis and carrying three radial arms which are evenly angularly spaced apart and define spherical bearing surfaces, a second element having a second axis intersecting the first axis and capable of making an angle therewith, said second element defining three pairs of raceways, intermediate elements disposed between said spherical bearing surfaces and said raceways, rolling members being interposed between the intermediate elements and the adjacent raceways, wherein the raceways provided on the second element are cylindrical surfaces having a roughly circular cross-section and generatrices parallel to the axis of the second element, the rolling members interposed between the intermediate elements and the raceways being balls.
According to other features of the invention:
in operating at an angle, each intermediate element undergoes an oscillating motion about the axis of the associated raceways;
each intermediate element has on its side facing the adjacent raceway a similar raceway, i.e. a roughly cylindrical shape having a circular cross-section and generatrices parallel to the axis of the second element;
the intermediate elements are bars defining on one side a spherical bearing surface cooperating with the complementary spherical bearing surface of the first element and on an opposite side a raceway for the rolling members;
the balls interposed between an intermediate element and an adjacent raceway are maintained by a cage;
said cage comprises end-of-travel means cooperative with end surfaces of the intermediate elements;
each cage comprises ball retaining means on the side opposed to the raceway of the second element;
means are provided for constraining each cage to travel through one half of the travel effected by the center of a spherical bearing surface of the first element;
these means comprise a gear journalled on a pivot laterally carried by the cage and engaged with two racks respectively carried by the intermediate element and the second element;
each intermediate element defines a raceway separated into two portions by an intermediate wall;
each intermediate element comprises a raceway divided into at least two segments each of which receives at least one ball, each segment being terminated at its two ends by a roughly spherical wall connected to the cylindrical surface of the segment of the adjacent raceway.